A typical example of a spintronic device is a magneto-resistance sensor. As shown schematically in FIG. 1, this includes seed layer 11, an antiferromagnetic (AFM) layer 12, outer pinned layer 13 (anti-parallel 2 or AP2), AFM coupling layer 14, typically, but not limited to, Ru, inner pinned layer 15 (AP1), spacer layer 16, free layer (FL) 17, and capping layer 18. Depending on whether spacer layer 16 is conductive or insulating (i.e. a barrier layer), the sensor is either a Giant Magneto-Resistance (GMR) device or a Tunneling Magneto-Resistance (TMR) device.
As recording densities increase, device sizes become correspondingly smaller. Consequently the sensor (or other spintronic device) has to continue having a high enough magneto-resistance (MR) ratio, as well as a low enough resistance.area product (R.A), for it to still have sufficient output amplitude and also for it to be suitable for future extendibility.
It is, however, becoming increasingly more difficult for MgO-based TMR devices to maintain their current high MR ratio in the lower R.A region. Current Perpendicular to the Plane (CPP) GMR or Confined Current Path (CCP) GMR devices have not yet been able to produce high enough MR ratios for them to take over as the future read head technologies. There is thus an urgent need for sensors that have higher output amplitude and/or a higher M.R ratio.
The present invention, as will be detailed below, discloses some novel methods for further enhancing the MR ratio.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 7,596,015 (Kitigawa et al) shows a free layer including an intermediate layer of Cu and/or Zn or Sn. (See col. 5, lines 58-63 free layer is the same as recording layer 12, and see col. 11, lines 1-15 for materials added to the recording layer—at least one of the materials including Cu, Zn, and Sn).
U.S. Pat. No. 7,223,485 (Yuasa et al) teaches an insertion layer in the free layer. (See col. 2-3 where the insert layer contains at least one element from Cu, Zn, O). K. Zhang et al, HT06-055 “a novel CPP device with enhanced MR ratio” and the reference therein. Y. Chen et al, “Spin-dependent CPP transport properties of ZnO/ferromagnet Heterostructures” Physics Letters A 303 (2002) 91-96